This familiar face once heated up the internet as the internet meme known as the Sarcopterygii, specifically the Sarcopterygian fish. It all started with a model displayed at the Museum of Natural History in Helsinki, Finland. Its unique and enigmatic expression reached the peak of popularity online, leading to a surge in memes, songs, models, games, and emojis. The Sarcopterygian fish has established itself as a beloved figure among the public, despite being a minor prehistoric creature. However, one disappointing aspect is that, despite its fame, there is a severe lack of information about it, and much of what exists is often incorrect. When were these creatures discovered? Why do they have such distinctive faces? And what led to their finless appearance? Today, we will scientifically explore the Sarcopterygian fish in this content.

I have prepared a scientific story about the Sakabambaspis, which once dominated the seas. It begins now. The year is 1986, and a fossil discovered in the Ordovician strata around the village of Sakaba in Bolivia, located 300 kilometers east of the Andes, is being studied. Researchers Pierre-Yves Ganiere, Alain Blieck, and Gabriela Rodrigo reveal that this is a fossil of an ancient fish's armor, and they name it Sakabambaspis. The name Sakabambaspis means the shield of Sakaba, and the species name ganierei is derived from the name of the discoverer Ganiere's mentor, the Paleozoic fish expert Philippe Janvier. However, to be honest, this fossil alone does not clearly indicate that it is a fish. So, how did they recognize the tadpole-like appearance of Sakabambaspis? The answer is simple: they found a more complete fossil. The first Sakabambas.

In a different layer where the fossils of the Spis were discovered, many fossils of the Saka Bamba Spis were found. In some cases, more than 30 individuals of a single fossil were discovered at once, which was truly a lucky find for paleontologists. But how did so many fossils come to be found together? Dr. Gani presents an interesting hypothesis regarding this. During the Paleozoic era, when the Spis lived, Bolivia was surrounded by a shallow sea, and there were rivers flowing into this sea. One day, due to a flood, a large amount of freshwater suddenly entered the sea, causing the Saka Bamba Spis near the river mouth to be unable to withstand the rapid changes in salinity, resulting in mass death. They were then buried by the sediment brought in by the flood. Thanks to this disaster that occurred hundreds of millions of years ago,

We have come to see the complete form of the sacabambas species. It's not just about its appearance; the discovery itself is quite remarkable. We will now begin a focused exploration of its various body parts, starting with the head. The head of the sacabambas species is surrounded by a shield-like armor, as the name suggests. Large plates cover the top and bottom, while several smaller plates protect the gills on the sides. This armor served as an important defense against predators like sea scorpions, which roamed the ocean at that time. The most striking feature is undoubtedly its face. While its eyes may appear somewhat foolish, the jaw, which differs somewhat from that of typical fish, is one of its major charms. For those who have seen my previous video on the evolution of jaws, you would know that jaws originally developed from the cartilage that formed the gills.

It was formed due to the deformation of the jaw. Before this evolution occurred, the mouth was simply a round hole. In fact, we can easily observe this shape in primitive fish like the lamprey and the hagfish. Fish without jaws are collectively referred to as agnatha. The Sakamba species also belonged to this jawless group. Unlike today's eel and lamprey, these creatures did not have teeth. However, they did have small bony scales in their mouths that covered the underside. The Sakamba species, lacking both jaws and teeth, likely lived by sucking in and swallowing small food items like plankton or organic debris floating in the water. Now, let's take a look at the body. The body is just as unique as the face, but we cannot find any dorsal, ventral, or pectoral fins on them.

cannot have it; it only has a tail fin. In fact, this is not a matter of historical accuracy, but rather because the evolution of pectoral and dorsal fins in fish occurred after the Ordovician period. Following the Ordovician, during the Silurian period, fish such as Tugiaspis and Atelaspis appeared, possessing pectoral or dorsal fins. Subsequently, jawed fish, known as gnathostomes, emerged, equipped with a variety of fins including pelvic and dorsal fins, and they continue to dominate the seas to this day. Meanwhile, the genus Sakaba has an interesting episode related to fins. Their only fin, the tail fin, has been a subject of debate, as there is evidence of changes in its morphology. The reason this fin has become a topic of controversy is that the fossils of Sakaba are well-preserved, but the tail fin's...

The only visible shapes were two points, and even those were slightly blurred at the tip of the tail. In this situation, Dr. Gani, who studied fossils, used the well-defined shape of the tail from one of the two specimens to reconstruct the tail of the Sakabambas piece. However, based on the previous reasons, scientists like Mark Wilson, who had doubts, presented counterarguments. Gani accepted this criticism and reconstructed the Sakabambas piece to resemble a tadpole's tail. It seemed that the debate about the shape of their tails had come to a conclusion, but then in 2006, a paper co-authored by Gani and Zhang was published, leading to a revision of the tail reconstruction. One of the issues with the specimen that best displayed the tail fin was that the back end resembled the head of another Sakabambas piece.

The researchers discovered that only the head part, which was covered, was slightly cracked open to observe a more complete view of the tail. As a result, it was revealed that there were very small fins at the tips of their tails, leading to a depiction of the fins above and below being of different sizes. From the discovery to the preservation, this creature has had quite a tumultuous journey. Also, for those who enjoy paleontology, there is another animal that likely comes to mind when looking at the Sakaba species: the Dunkleosteus. Although their appearances differ slightly, both are similar in that they are covered with hard armor on their heads. However, there is a clear difference between the two. First, the Sakaba species is a type of armored fish, while the Dunkleosteus is a placoderm, which is known for being one of the first fish to develop bones.

Various types of fish with bones covered in scales or armor appear. The Sacababas piece is one of them. Long before the emergence of fish with bony jaws, there existed a collection of many types of fish from the class of bony fish, which were adorned with bony armor and scales. This collection is referred to as placoderms. However, this term merely groups together the awkward ones between the eel and the ray-finned fish for convenience, even though each type of placoderm belongs to a different lineage, and it is not commonly used nowadays. On the other hand, the genus Dunkleosteus, which belongs to the placoderm fish, includes some of the earliest jawed fish to appear. The placoderm fish, unlike the jawless fish, represent a different level of evolution. In simple terms, when we express the early evolution of vertebrates, the Sacababas piece can be roughly positioned here, near Dunkleosteus. That's all there is to it.

The armored fish, Sacabambaspis, belongs to a group known as the jawless fish. Although the Dunkleosteus had a destructive jaw, Sacabambaspis did not, but it was the first to have bony structures in the head among vertebrates. Particularly, Sacabambaspis is the oldest species preserved as a complete fossil among early fish. Contrary to the humorous depictions, these creatures are treasures in paleontology. 

Now, a question may arise. If vertebrates have bony structures, then it would make sense for them to develop from the back first, but since the first bones are found around the head, does that mean armored fish lack vertebrae? The answer is yes; armored fish do not have vertebrae. There are three main types of substances that vertebrates use to form their skeletons: notochord, cartilage, and bone. Primitive species like the lamprey represent these early forms.

Vertebrates are characterized by having a backbone made of cartilage and a notochord, but they do not have true vertebrae. This was also the case for the armored fish, Sacababaspis. It was not until millions of years later that true vertebrae were created by introducing calcium phosphate into the design of the spine. What is even more interesting here is that although the armor of Sacababaspis and our vertebrae may look similar, they are actually different types of bone. Bones can be classified into two categories based on their formation process. The type that armor belongs to is called membrane bone, while vertebrae are classified as cartilage bone. Membrane bones are formed through a simple mechanism where osteoblasts directly build the bone, whereas cartilage bones are formed through a more complex process where a cartilaginous model serves as the foundation, and later, osteoblasts replace the cartilage with bone. Naturally, vertebrates came first.

진화시킨 것은 막골이고, 앞서 갑주어 보듯 뼈는 머리 쪽에서 먼저 생겨났습니다. 그래서 오늘날 척추동물의 머리뼈 대부분이 막골이고, 몸통 뼈의 대부분은 연골 내 골의 형태입니다. 같은 뼈라도 진화사에 따라 그 형성 과정이 다르다는 사실이 참 신기하지 않나요? 참고로 더 신기한 것은 사카바 스피스 뼈에서 이빨의 기원을 엿볼 수 있다는 사실입니다. 사카 반바 스피스 갑주의 단면에서 맨 꼭대기를 보시면, 보통의 뼈와 다른 아주 특수한 물질들이 있습니다. 바로 상아질과 에나멜입니다. 로이드조지 뼈보다 치밀하고 단단한 이 물질들은 갑주의 표면에 오돌토돌한 돌기들을 형성하는데, 이 돌기들을 다른 말로 오돈토드라 합니다. 오돈토드 이름은 생소하지만, 이게 바로 우리 치아의 기원입니다. 사람 치아의 구조를 볼까요? 상아질이 있고, 그 위에 에나멜이라 불리는 법랑질이 덮고 있죠. 보시다시피.

The basic structure is similar to that of the primitive odontodes. Of course, the primitive odontodes of early fish did not directly evolve into our teeth. The odontodes, surrounded by enameloid, later evolved into fish scales and teeth. When we reach bony fish among the various types of fish, a new substance called enamel appears. Among these, terrestrial vertebrates that ventured onto land completely lost enameloid in their teeth. It is said that the ganoid scales of vertebrates without enamel retain the primitive features of odontodes well. The structure where enameloid covers the dentin is very similar to the teeth of sharks. Thus, from simple forms like Sacabambaspis, jaws and fins developed, and new types of bones were formed, leading to the emergence of creatures similar to modern fish like placoderms.

And for an eternity, nature did not leave things as they were; it created bony fish that simultaneously possessed cartilage and bone, while also causing all bones except for teeth and vinyl to regress back to cartilage. This is the evolution story that began with the cute fish, the Sacabass. What did you think? The fact that there are fascinating narratives in the fossil records of fish, like a drama, might be the true charm of paleontology. Science is a window to the world. So far, this has been Science Dream. Oh, and I have another book out now. It's called What Do You Imagine About Becoming a Science Creator? It's a related book that contains my know-how on creating science content and various experiences from my life as a science journalist to becoming a YouTuber. Even if you're not a YouTuber, if you're interested in producing science content in various forms, such as writing or video, this book is for you.

이 직업에 관심 있는 청소년들이 있다면 한 번쯤 읽어보면 좋을 것 같습니다. 그리고 과학 크리에이터 직업을 주제로 그래비티, 개놈, 아톰 익스프레스 시리즈를 펴낸 제가 정말 좋아하는 조진호 작가님과 함께 북토크도 진행합니다. 날짜는 10월 31일 7시이며, 장소와 예매 관련 내용은 고정 댓글에 적어둘 테니 많은 관심 부탁드립니다. 감사합니다.

당신이 몰랐던 사카밤바스피스의 기묘한 생물학!(ft.어류의 진화)

과학으로 재미와 지식을 더해 드리는 채널입니다.
한 때는 과학을 좋아했던, 지금도 과학을 좋아하는, 
그리고 앞으로 과학을 좋아할 사람들이 제 채널과 함께였으면 합니다.
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